We shall study regulation of Protein biosynthesis and nucleic acid metabolism during embryogenesis to gain a firmer understanding of molecular mechanisms which underlie such developmental phenomena as differentiation and growth. Our attention shall be focused on regulation at the translational and post-translational levels because it is at these levels that the protein biosynthetic machinery appears to be controlled during the initial stages of development. In particular we hope to confirm and to extend our present knowledge of the macromolecular structure of the gene for rRNA. This added information will be used to further the investigation of regulation of the synthesis and processing of rRNA, the assembly of the 60S ribosomal subunits and the association of the tightly bound polysome-membrane complexes. In addition we shall complete our current characterization of the kinds of protein made on "free", loosely bound and tightly bound polysomes at the several stages of embryogenesis. The role of effector molecules such as high affinity folate binders on nucleic acid and protein synthesis and modification will also be examined. BIBLIOGRAPHIC REFERENCES: Kamen, Barton A., P.L. Takach, R. Vatev and J. Douglas Caston (1976). A rapid, radiochemical-ligand binding assay for methotrexate. Anal. Biochem. 70:54-63. Kamen, Barton A. and J. Douglas Caston (1976). Folate and Coated Charcoal Reagent. Clin. Chem. 22:1409-1410.